The present invention relates to silicone polymers, more specifically to polyether substituted silicone elastomers.
The personal care industry thrives on being able to deliver multiple performance products based on a mixture of several components, each having performance characteristics important to the final formulation. One need in preparing these formulations is for materials that can both enhance performance as well as compatibilize and hold together in the formulation the various components of the formulation.
Recent technology has produced several crosslinked polydimethylsiloxane elastomers that are capable of absorbing cyclic and low molecular weight silicones useful in the personal care industry. The use of alpha-omega diallyl terminated polyethers as a chain extending component in making crosslinked siloxane elastomers has been shown (see, for example, U.S. Pat. No. 5,138,009; U.S. Pat. No. 5,412,004; U.S. Pat. No. 5,236,986). In one variation, these products suffer from the need to synthesize polyethers with an allyl functional group at both ends, and this is expensive because it requires a separate synthesis step to add the second allyl functional group. In addition, since the diallylpolyether is used as a chain extender, the amount that can be added to the composition is severely restricted by the need to form a polymer network. In a second variation, a polyether/hydrido substituted siloxane prepared in a separate, difficult and expensive reaction is used to introduce the polyether functionality. The present invention employs the use of a single vessel reaction to produce a uniquely structured elastomer and the polyether functionality is introduced using commercially available allyl started polyether compounds.
The synthesis of organically crosslinked siloxane elastomers that have been substituted with mono and diallyl terminated polyethers has been demonstrated (see, for example, U.S. Pat. Nos. 5,889,108; 5,811,487). These elastomers suffer from the requirement of having an alpha,omega-diolefin as the chain extender and a diffuse silylhydride crosslinker. This creates a different structure which may lose some of the desirable siloxane properties. Such organically crosslinked polymeric siloxanes appear to have significantly less absorbing efficiency relative to all siloxane based elastomers utilizing a higher functionality crosslinker.
A curable composition comprised of a branched, allylfunctional polyether, a branched, hydridosiloxy terminated polyether and a catalyst has also been disclosed (see, for example, U.S. Pat. No. 4,877,854). This composition requires difficult to make branched and allyl functional polyethers which determine the crosslink density, leaving no capability to control the amount of polyether content. The second component (siloxane) is equally difficult and expensive to make and ultimately limiting in the design flexibility to control performance. This system for making dental impressions forms a solid plastic unsuitable for making the small particle size required for personal care applications.
The structures defined in the above referenced patents are highly hydrophilic as a result of the total methyl substitution on silicone. Because of the hydrophilic nature, they are at best compatible with selected non-polar organic and siloxane based materials. This is a limiting feature as many formulated compositions useful in the personal care industry include water, polar organic materials such as low molecular weight alcohols, or a combination of both.
What is needed is a crosslinked siloxane elastomer which is efficient in absorbing low molecular weight silicones, has a pleasant feel and can be compatibilized or emulsified with water, polar organic materials, or a combination thereof.
In a first aspect, the present invention is directed to a cross-linked polyether substituted silicone elastomer, comprising the cross-linked hydrosilylation reaction product of:
(i) an alkenyl functional silicone compound;
(ii) a silylhydride functional siloxane; and
(iii) an allyl started, hydrogen, alkyl, aryl or acyl terminated polyether compound.
The silicone elastomer is hydrolytically stable, in that the polyether substituents are attached to the elastomer via Sixe2x80x94C bonds having good hydrolytic stability and can be easily and economically prepared in a single step. As used herein, the terminology xe2x80x9chydrolytically stablexe2x80x9d means a tendency not to undergo changes in structure, such as, for example, cleavage of bonds, as a result of exposure to moisture.
Preferably, the silylhydride functional siloxane contain a sufficient number of Sixe2x80x94H groups to hydrosilylate the desired amount of allyl terminated polyether molecules with at least 1.5 SiH groups per molecule remaining for crosslinking with the alkenyl functional silicone compound.
Preferably, the alkenyl functional silicone compound contain at least 1.5 alkenyl units per molecule and has alkenyl substitutions on any or all of the M, D or T units. The number of available functional units on the SiH and alkenyl functional sites must be sufficient to form a gel on polymerization in a volatile siloxane.
This invention makes use of allyl started polyethers that may be commercially available and made without a second addition step. Since they are monofunctional, they can be flexibly introduced into the crosslinked siloxane elastomer while retaining the polymer network structure.
In a second aspect, the present invention is directed to a method for making a cross-linked polyether substituted silicone elastomer, comprising forming the hydrosilylation reaction product of:
(i) an alkenyl functional silicone compound;
(ii) a silylhydride functional siloxane; and
(iii) an allyl started, hydrogen, alkyl, aryl or acyl terminated polyether compound.
In a third aspect, the present invention is directed to a silicone composition, comprising a liquid medium, said liquid medium comprising an organic liquid, a silicone fluid or a mixture thereof; and a silicone elastomer of the present invention dispersed in the liquid medium. The elastomer of the present invention exhibits improved compatibility with organic liquids. As used herein, the xe2x80x9ccompatibilityxe2x80x9d of an elastomer with a liquid refers to the ability to form a stable dispersion of the elastomer in an organic liquid.
In a fourth aspect, the present invention is directed to an emulsion comprising an emulsion of a first liquid phase and a second liquid phase and a silicone elastomer of the present invention dispersed in the emulsion.
In a fifth aspect, the present invention is directed to a personal care composition comprising a silicone elastomer of the present invention.